CH. V SERIES-WOUND MOTORS 109 



curves, and let og be the maximum possible current when 

 the speed is nothing : from g draw any line gfc cutting the 

 induction curves in /and c. Then fd and cb will repre- 

 sent the values of the induction factors in the two motors 

 when A is drawing a current equal to ob, and 7? is drawing 

 a current equal to od. Let fd and cb cut the loss line lig 

 in e and a. Then, since ab and ed represent the induced 

 tensions in the two motors, we see that the speed of A is 

 ab divided by be, and the speed of B is de divided by 

 df, and these ratios are by construction equal to one 

 another, hence the two motors are running at the same 

 speed. We can then find the ratio of the induced ten- 

 sions of two coupled series-wound motors in parallel, with 

 unequal induction curves and equal resistances, by draw- 

 ing lines from the point g cutting the curves at different 

 angles, and the vertical ordinates at the points of inter- 

 section give the required ratio. 



When two motors with unequal induction curves 

 have no residual magnetisation, the difference between the 

 induced tensions increases with the load and decreases with 

 the speed, becoming nothing when the speed is infinite. 

 If, however, there is residual magnetism in one or both 

 of the motors, there is generally a certain speed for 

 which the difference is greatest. 



In Fig. 27, A B and A'B' represent the magnets and 

 armatures of two motors connected in parallel. If the 

 points a and c are joined, we have conditions which may 

 prove very troublesome. If the resistances of the magnet 

 windings are equal in the two machines the currents in 

 the magnets will be equal, so that whatever the motors 

 are doing the current from the line will be equally 

 divided between the two magnets. Suppose now that 



